1. Field of the Invention
The present invention relates in general to a refrigerant transporting hose, and in particular to such hoses suitable for use as pipings of car coolers, air conditioners and the like which are employed in automotive vehicles.
2. Discussion of the Prior Art
There is known a hose for transporting a refrigerant such as freon (fluorohydrocarbon and chlorofluorohydrocarbon). The hose has an integral multi-layer construction consisting of an inner tube, an outer tube located radially outwardly of the inner tube, and a reinforcing fiber layer interposed between the inner and outer tubes. The inner tube is formed of acrylonitrile-butadiene rubber (NBR) or chlorosulphonated polyethylene (CSM), while the reinforcing fiber layer has a mesh structure formed by braiding organic yarn such as polyester fiber, rayon fiber, nylon fiber, etc. Meanwhile, the outer tube is formed of ethylene propylene diene rubber (EPDM) or chloroprene rubber (CR).
Being formed of rubber except for the reinforcing layer, the multi-layer hose has a high flexibility. Due to this characteristic, the hose can be handled with ease, for example in providing rubber piping. In addition, the hose is free from deterioration due to harmful metallic substances such as metallic ions and/or metal chlorides originating from metallic piping used in a refrigerant or coolant circulation system.
However, rubber materials generally have a comparatively high gas permeability, that is, low resistance to gas permeation therethrough. Accordingly, the conventional rubber hose suffers from the problem that the refrigerant (e.g. freon) circulating therein leaks through the wall thereof into ambient atmosphere, so that the refrigerant is progressivelY reduced in amount. In other words, the refrigerating or cooling capability of a system employing the rubber hose is comparatively rapidly lowered during a period of service, and gas charging (charging of refrigerant) must be conducted frequently to maintain satisfactory performance of the system. Meanwhile, nowadays there is an environmental problem that flon adversely affects the ozone layer of the earth atmosphere. Thus, it is a great demand for a refrigerant transporting hose having improved resistance to gas permeation therethrough. The conventional rubber-based hose exhibits excellent flexibility and excellent resistance to harmful metallic substances, but is unsatisfactory in resistance to permeation therethrough of refrigerant.
In the above-indicated situation it has been proposed to provide a hose the inner tube of which includes a layer formed of a resin having high resistance to refrigerant permeation. Polyamide such as nylon 6, nylon 66, or copolymer of nylon 6 and nylon 66 is used for forming the resinous layer. Such a hose has improved resistance to refrigerant permeation, but is unsatisfactory in flexibility and resistance to harmful metallic substances. Accordingly, this hose is not suitable for practical use. Since the polyamide is very effective against refrigerant permeation, it is possible to reduce the thickness of the resinous layer to a considerable extent. Even in this case, however, the hose is low in flexibility as compared with the conventional rubber hose.
Furthermore, in the case where other polyamides such as nylon 11 and nylon 12 are used for forming provide a layer of an inner tube of a hose, the hose produced has a high resistance to harmful metallic substances, but is lower in resistance to refrigerant permeation than the hose having a layer formed of the previously-indicated polyamide such as nylon 6 or nylon 66. Consequently, the layer formed of nylon 11 or nylon 12 must be thickened as such, to have a comparable resistance to refrigerant permeation. The hose having the thickened resinous layer suffers from an extremely reduced flexibility, and is not suitable for practical use.
As emerges from the foregoing, none of the conventional refrigerant transporting hoses is satisfactory in quality, in particular in view of recent great demand for hoses having more excellent resistance to refrigerant permeation therethrough.